The invention relates to an optoelectronic semiconductor device comprising a radiation-emitting semiconductor diode of which an exit surface for the generated radiation is provided with a coating.
Such a device is particularly suitable for use as a radiation source in, for example, an optical glass fibre system, an optical disc system, and a bar code reader. In the application first mentioned, the emission wavelength often lies between 1 and 1.5 .mu.m, in the other applications often between 0.6 and 0.9 .mu.m. The semiconductor material systems corresponding therewith are InGaAsP/InP and (Al)GaAs/AlGaAs or InGaP/InAlGaP, respectively.
Such a device with an (AlGa)As diode laser as the radiation-emitting diode is known from the article "Analysis of Rapid Degradation in High-Power (AlGa)As laser diodes" by W. J. Fritz published in IEEE Journal of Quantum Electronics, vol. 26, no. 1, January 1990, pp. 68-74. The device described therein comprises a diode laser tested in a dry nitrogen atmosphere or in vacuum, the mirror surfaces acting as exit surfaces for the radiation generated by the diode laser being provided with an aluminium oxide or aluminium oxide-silicon coating which is impermeable to gases. It was found that a layer rich in carbon is deposited on this coating during operation of the diode laser, which layer originates from organic impurities contained in the flux and flux cleaning liquid used during soldering of the diode laser. The diode laser is not stable in this case, i.e. the output power decreases (or fluctuates) strongly in time, for example, owing to changes in the (effective) reflection of the radiation at the mirror surface provided with the coating. Strongly improved characteristics were obtained by means of more stringent cleaning instructions and selection on the basis of the hydrocarbon content.
A disadvantage of the known device is that it is comparatively difficult to manufacture owing to the stringent cleaning requirements, and accordingly is comparatively expensive. The price of the known device is also adversely affected by the reject percentage in the selection process.